Journal of Coastal Research, Special Issue 56, 2009 Journal of Coastal Research SI 56 1395 - 1399 ICS2009 (Proceedings) Portugal ISSN 0749-0258 Effect of flooding the salt pans in the Ria de Aveiro A. Picado † , J. M. Dias † and A. B. Fortunato ‡ † CESAM, Physics Dept., University of Aveiro, 3810-193 Aveiro, Portugal ana.picado@ua.pt joao.dias@ua.pt ‡ Dept. de Hidráulica e Ambiente Laboratório Nacional de Engenharia Civil Av. Do Brasil, 101, Lisboa 1700-066, Portugal afortunato@lnec.pt ABSTRACT PICADO, A., DIAS, J. M., FORTUNATO, A. B., 2009. Effect of flooding the salt pans in the Ria de Aveiro. Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium), 1395 – 1398. Lisbon, Portugal, ISBN 0749-0258. The Ria de Aveiro, a mesotidal lagoon located on the Northwestern Portuguese coast, is characterized by large areas of intertidal flats and a web of narrow channels. The lagoon has a large area of mostly abandoned salt pans, whose progressive degradation is caused by the lack of maintenance and by the strong currents which erode their protective walls. The shallow water model ELCIRC was implemented and calibrated for the Ria de Aveiro in order to study its hydrodynamics, with special emphasis on the effect of the destruction of the salt pans protective walls. The calibration was performed by adjusting the bottom friction coefficient, through the comparison between measured and computed time series of surface water elevations at several stations within the lagoon. Harmonic analyses of these data were performed in order to evaluate the models accuracy. An assessment of root mean square errors and skill showed that a good calibration was achieved. Once calibrated, ELCIRC was used to characterize the hydrodynamics of the entire lagoon and the channels around the salt pans under different scenarios (present bathymetry and a projection of the bathymetry resulting from the walls destruction). An extreme destruction of the salt pan walls would result in a significant increase of the inundation area in Ria de Aveiro, as well as in changes of the global and local hydrodynamic regimes. In summary, this study reveals how the increase of the flooded area in estuarine lagoons can affect tidal propagation, including the increase of tidal currents, tidal prism and tidal asymmetry. The long-term implications of the salt pans inundation are discussed based on the results. ADITIONAL INDEX WORDS: ELCIRC, tidal asymmetry, tidal prism INTRODUCTION The Ria de Aveiro (Figure 1) is a coastal lagoon located on the Northwestern Portuguese coast, with a surface area of about 83 km 2 at high tide (DIAS et al., 1999). The lagoon has a very irregular geometry, being characterized by narrow channels and extensive intertidal flats areas, namely mud flats and salt marshes. The Ria de Aveiro has a large area of abandoned salt pans, whose degradation is caused by the lack of maintenance and by the strong currents that erode their protective walls. The main aim of this study is to understand the consequences of the salt pan walls collapse on the Ria de Aveiro hydrodynamics, that results in an increase of the flooded area. To evaluate the impact of bathymetric changes in systems like this, several future scenarios were simulated, in which salt pans walls destruction was assumed. These simulations were performed with the shallow water numerical model ELCIRC (ZHANG et al., 2004). The model was previously implemented in Ria de Aveiro (OLIVEIRA et al., 2006), in order to study its inlet dynamics in terms of tidal propagation, as well as the variability of tidal asymmetry in the upper and lower lagoon. The horizontal grid developed by these authors is inadequate for the present study, because the central area of the Ria de Aveiro has low resolution. Hence, the existing grid was improved by adding and refining several channels, mainly in the central area of the lagoon, where salt pans are located. The paper is divided into five sections besides this introduction. The second section describes the characteristics and problems of the study area. The next section presents the methodology. The hydrodynamic model calibration is presented in the fourth section and the evaluation of the hydrodynamic changes under the partial collapse of the salt pans walls of the Ria de Aveiro is presented in fifth section. The paper closes with some concluding remarks. STUDY AREA The Ria de Aveiro is a shallow water mesotidal lagoon located in Northwest coast of Portugal (40º38’N, 8º44’W). The lagoon has a maximum width of 10 km and its length measured along the longitudinal axis is 45 km (DIAS AND LOPES, 2006a,b). The average depth of the lagoon relative to the chart datum is about 1 m, except in navigation channels where dredging operations are frequently carried out. Due to the small depth and to the significant tidal wave amplitude there are zones, especially along the borders of the lagoon and its central area, which are alternately wet and dry during each tidal cycle. The lagoon is mesotidal (tidal amplitude at the inlet ranges from 0.6 m in neap tides to 3.2 m in spring tides – average range of 2 1395